Method of heat treatment of a steel product

ABSTRACT

A METHOD OF HEAT-TREATING AND HARDENING A STEEL PRODUCT SUCH AS A TOOTHED WHEEL AND SIMILAR STRUCTURAL ELEMENTS, REQUIRING A HARDNESS AND ABRASION RESISTANCE ON PORTIONS OF ITS WORKING SURFACES INCREASED IN COMPARISON TO THE HARDNESS AND ABRASION RESISTANCE OF THE REMAINING PORTIONS COMPRISING THE STEPS OF PROVIDING ON THE SURFACE OF SAID PRODUCT AT LEAST ONE GROOVE SEPARATING THE SAID SURFACES OF PORTIONS OF REQUIRED INCREASED HARDNESS FROM THE REMAINING SURFACES; LOCALLY HEAT-TREATING THE SAID PORTIONS OF THE SURFACES REQUIRING AN INCREASED HARDNESS AS THEY ARE DIVIDED BY SAID AT LEAST ONE GROOVE AND SUBSEQUENTLY HARDENING BY QUENCHING THE HEAT-TREATED PORTIONS LEAVING THE REMAINING PORTIONS WITH ITS ORIGINAL HARDNESS AND ABRASION RESISTANCE.

May 11, 1971 SHINNOSUKE FUNAKUBO 3,573,512

METHOD OF HEAT TREATMENT OF A STEEL PRODUCT Filed May 17, 1968 Fig.1Fig.2

TEMPERATURE mvemon SHINNOSUKE Fummm ATTORNEY I 1 BY WW United StatesPatent O 3,578,512 METHOD OF HEAT TREATMENT OF A STEEL PRODUCTShinnosuke Funakubo, Tokyo, Japan, assignor to Funakubo Seikyo KahushikiKaisha, Tokyo, Japan Filed May 17, 1968, Ser. No. 730,120 Claimspriority, application Japan, May 25, 1967, 42/ 32,789 Int. Cl. C21d 9/32US. Cl. 148-147 6 Claims ABSTRACT OF THE DISCLOSURE A method ofheat-treating and hardening a steel product such as a toothed wheel andsimilar structural elements, requiring a hardness and abrasionresistance on portions of its working surfaces increased in comparisonto the hardness and abrasion resistance of the remaining portionscomprising the steps of providing on the surface of said product atleast one groove separating the said surfaces of portions of requiredincreased hardness from the remaining surfaces; locally heat-treatingthe said portions of the surfaces requiring an increased hardness asthey are divided by said at least one groove and subsequently hardeningby quenching the heat-treated portions leaving the remaining portionswith its original hardness and abrasion resistance.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates to a method of heat treatment of a steel product, particularlyworking parts of machines such as a toothed wheel.

Description of the prior art Most of toothed wheels and other steelworking parts of machines are essentially required to be hardenedextremely and locally at their working portion such as a tooth portionof a toothed wheel, and are to retain toughness at their other bottom orcentral portions. The conventional hardening, for satisfying the aboverequirement, has been conducted in the way that for example, a heatedchisel is cooled locally at a predetermined hardening portion with aquenching agent, and after that, tempered at said portion with excessheat other portions remaining not cooled. The methol is applicable tochisels and tools, the hardening portions of which are straight, but notto toothed wheels, the hardening portions of which extend radially. Forimproving the abrasion resistance on surfaces of the work portions ofsteel products, a flamehardening or high-frequency hardening has beenemployed for casehardening around their working surfaces. This method isdifficult to use in the surfaces locally and limitedly.

SUMMARY OF THE INVENTION An object of the present invention is, hence,to provide a method of heat treatment of a steel product, particularly atoothed wheel and other structural elements of machines, havingpredetermined hardening portions capable of heating and hardeninglocally and limitedly with other portion remained unhardened andreducing to the minimum the probability of distortion which has beenencountered on heated products of the prior art.

The principle of the present invention is, therefore, to provide amethod of heat treatment of a steel product, such as a toothed wheel andsimilar structural elements, which comprises providing one or moregrooves between the portions to be hardened and other portions not to behardened, and subjecting said firstly-mentioned portion "ice to aheating atmosphere. The heat applied to said firstlymentioned portion ishindered from transmission to said secondly-mentioned portion, becauseof the existence of said grooves, and said secondly-mentioned portionremains unaffected by the 'heat treatment.

DESCRIPTION OF THE DRAWINGS In the accompanying drawings showingpreferred embodiments of a structural element to be heated by theheating method of the present invention.

FIG. 1 shows a plan view of a toothed wheel provided with a heattransmission inhibiting groove of the present invention to be treated bya heating method of the present invention;

FIG. 2 shows a sectional view taken along the line IIII of FIG. 1;

FIG. 3 is an explanatory diagram showing a transmission of heat appliedto the. toothed wheel from the direction of a projected portion, to behardened and FIG. 4 is a partial view in perspective showing anotherembodiment of the toothed wheel treated by the heating method of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, a toothedwheel 1 is shown having a number of teeth 2 provided with a hole 4 for acentral axis. On each end surface of said toothed wheel 1, a circulargroove 3 is provided around the outer periphery of the portion to behardened and at a certain distance therefrom. When heat generated, forexample by a highfrequency electromagnetic field or a flame, is appliedto the tooth portion of said toothed wheel from the direction of theprojected portion, said tooth portion, appreciably, is heated rap-idly,but the remaining portion between the axis and the groove 3 remains notheated. A distribution of the heating temperature onto the toothed wheelis shown in FIG. 3, the diagram of which is based upon the temperingcolor surface as it appeared on each surface of toothed wheel.

Apparently the groove 3 serves to prevent transmission of the heatapplied to the tooth portion in the direction of the centre of axis, butthis premise is not clear. In heating by a high-frequencyelectromagnetic field, the groove 3 seems to work to cut off line ofmagnetic force.

If the thus heated toothed wheel is quenched, said toothed wheel ishardened only at the tooth portion, but remains unhardened at theportion nearer to the axis or the basic portion.

In another embodiment shown in FIG. 4, plural grooves 3 are providedradially inwardly of the teeth of the toothed wheel and extending in theaxial direction thereof.

The deeper the groove the greater is the hindrance of heat transmission,but an excessive increase in depth of the groove would cause aconcentration of stress onto the groove, leading to damage or breakdownaround the grooved portion during practical application of the toothedwheel. The most efficient groove therefore has a depth which does notinterfere with maintaining the basic portion confined by the groove at atemperature below the transformation point of the toothed wheel, if thetemperature aroundthe tooth portion reaches to the transformation point.

What is claimed is:

1. A method of heat treatment and hardening of a steel product, toprovide it with a hardened working portion having a working surface anda remaining portion with its original hardness, such as a toothed wheeland similar structural elements which comprises the steps of providingat least one groove in the surface of said product, between the saidworking portion to be hardened and the remaining portion, which is notto be hardened;

subjecting said working surface portion to be hardened to a heatingtreatment and subsequently hardening said working portion by quenchingthe heat applied to the said working portion is hindered by said groovefrom transmission to the remaining portion, and the said remainingportion is substantially unaffected by the heat treatment.

2. A method of heat treatment of a steel product as claimed in claim 1,the heat being applied to said working portion by high-frequencyheating.

3. A method of heat treating a steel product as claimed in claim 1, theheat being applied at a temperature above the transformation point ofsaid working portion.

4. A method of heat treating a steel product as claimed in claim 1, theheat being applied by a flame.

5. A method of heat treating a steel product as claimed in claim 1, saidsteel product comprising a gear with wheel teeth, said groove being anannular groove provided on each face of the gear wheel radially inwardlyof the teeth.

6. A method of heat treating a steel product as claimed in claim 1, saidworking portion of said product being a tooth of a gear, said groovebeing an axially extending groove provided on each side of the tooth atits base.

References Cited UNITED STATES PATENTS 2,430,005 11/1947 Denneenet al.148-149 RICHARD O. DEAN, Primary Examiner US. Cl. X.R.

